I know there is much argument surrounding the use of aftermarket filters and EF airbox lids.

Here are some excerpts from last weeks Autospeed tech articles on the negative boosts and restrictions on the bog stock EF GLi air intake on their latest project car.

Going by the article, all tests are made in 2nd gear at full throttle upto 5000rpm.

"So for a standard car, the Falcon certainly doesn’t have a bad air intake. But there were still 16 inches of water of pressure drops through the intake system – and there doesn’t have to be any!"

"So (and this is the classic case that I love repeating each time we do a story like this!), by looking at the measured pressure drop after the filter (7.2) and the pressure drop before the filter (6.2) we can see that the pressure drop across the (new) filter is just 1 inch of water, or 0.036 psi! In fact, as it is always the way when you measure pressure drops, the filter contributes stuff-all to the total intake flow restriction. In all the testing we have done, we have never seen a factory filter contributing more than a trivial amount of restriction to the total – never! So, upgrading the filter in the standard airbox is a complete waste of time."

"So what mods should I do? The pressure drops caused by the other sections of the intake can be seen in the table, but it’s easier to see when it’s graphed. The chief hairy monster is the airbox exit – over the few centimetres between the inside of the airbox and the outlet duct, there’s a pressure drop of 6 inches of water - that’s nearly 38 per cent of the total intake restriction! But what about the previous flowbench testing? Well, apologies to those who have followed that test in the modifications they have done on their cars, but I don’t reckon it stands up to scrutiny. The outlet duct of the EF airbox is the smallest cross-sectional area of the intake system and it creates the greatest pressure drop. That means it flows badly!"

"We measured the pressure drop at various points through the system to calculate the contribution of each part. But we missed one. Look at the last line in the table above – the intake of the snorkel had a pressure drop of 3.2! That means the air is not able to adequately flow through to the mouth of the snorkel – there’s a negative pressure hiding in the gap between the bonnet and the bumper! The bastard!"

"The results of the pressure testing stacked-up reasonably well with the cross-sectional areas we measured last week. The exception – and it’s an important one – is the gap between the bonnet and the bumper/headlights (despite calculating out as a large cross-sectional area) imposes quite a major flow restriction – in fact, 20 per cent of the total. "

Make of it what you will. But it does make for an interesting test.

And it can go to show that even the "best flowing airbox lid of the lot" is a major restriction in the overall intake.

I eagerly await this weeks issue where they will describe fixes to eliminate some of these restrictions. I say eagerly as it will save me t he trouble of having to do these tests myself, which I failed to do during my holidays.

16" of water or 4kpa - spot on the restriction I measured in the manifold with the EF intake pipes a few months ago. The thing I found is that even when the intake was modified or removed completely that the manifold vacuum was not affected all that much. Will be interesting to see if they find the same thing.

I found it funny, seeing as some people had sworn black and blue the EF lid was better, off the results of the flowbench.

Including autospeed which is shocking because we all know they are never wrong

Interesting that they are quick to backstep on their previous findings though. Both the EF and later airboxes have similar restrictions around the same point (the EF's restriction is the narrowing of the pipe inside the airbox, presumably on the later ones it will be the narrow pipe at the edge of the airbox). I personally dont think their new results are all that relevant to the old.

In any case as most people know there are going to be minimal gains from swapping between them anyway.

This filter comparison might not be accurate when compared too the 6cyl falcon engines and intakes. But it's just a bit of info i found interesting...

it's in issue 104 of ZOOM

they did the test on their project Cyborg (mirage) FWD drag car and all tested were carried out in sucession on a Dyno Dynamics Dyno

Standard - 132.7 KW

Pipercross - 132.8 - $399

BMC carbon - 132.9 - $649

Drift Stainless - 133.3 - $100

Driftbitz Stainless - 133.7 - $66

K&N - 133.9 - $110

BMC F1 - 134.1 - $160

SAAS - 134.6 - $30

Driftbitz carbon - 134.6 - $33

JR - 134.9 - $105

HKS superflow - 134.9 - $195

NO FILTER - 135.1 - $0

Apexi - 135.3 - $120

Trust Arinx -135.9 - $155

Drift Urethane (Blue) - 136.2 - $36

cheers...

How can having filter be better than not having a filter???

Well theoretically, the filter could have some sort of bellmouth inside it, therefore being better then just a straight cut pipe, however i am leaning towards it being simply the fact that chassis dynos cannot get results that repeatable, and a few kws error either way is not out of the question.

i find it a little hard to beleive that the cheapest ura thane job equatesto the highest kw you should really be seeing the whole dyno sheets and wat tune it has in it and was it the same same driver for every test on the rolling road many factors many variables . I am not taking the piss but lets be realistic unless its a 50 000 dolar race come streeter who is going to worry about 0.1 of a kw . every day driving throws up so many variables your probably going to lose 5 kws sitting behind some horrible 4wd with its exhaust sitting right next to your air intake anyway. articles can be so cruel and give people such false hope.your post is interesting none the less good luck with your testing